In the dyeing industry, it is customary to color cloth by submerging it in a bath containing a solution of dye maintained at or near the boiling point. The cloth is then taken from the solution and washed to remove the excess dyeing solution still held by the cloth. The color is then fixed using a variety of well-known techniques.
This process, fundamentally unchanged since man first dyed cloth, suffers from a number of serious disadvantages. For example, a great amount of energy is expended in maintaining the bath at or near its boiling point. Another disadvantage is the uneconomical use of the dye. After the dyeing is completed, and the cloth removed from the bath, the remaining bath results in a significant watse of dyeing compound. Still yet another disadvantage in conventional dyeing processes is the amount of pollution created by the disposal of the remaining bath. Any reduction in the quantity of dye discharged is especially important due to the fact that chemical dyes are among the most difficult waste products to treat. The development of clean dyeing techniques has become increasingly important with the passage of the Federal Water Pollution Control Act Amendments of 1972 (Public Law 92-500). This law calls for goals of water quality which are to culminate in zero pollutant discharge by 1985.
Although extensive research is now being carried on with respect to many phases of the dyeing operation, the same basic technique, namely, dissolving the dye in a liquid, applying it to the fabric and fixing it, remains the same. An exception to this general rule has been the attempt to apply dye by vapor-phase dyeing, in which disperse dyes are applied in a gaseous form to various synthetic fabrics. However, the necessity of maintaining elevated temperatures in the presence of a high vaccum rules out this possibility as impractical, at least for the present time.
Although some attempt has been made to color fabric by the electrostatic transfer of specialized dyestuffs, as far as is known, no commercial usage of such a process has resulted. For example, in U.S. Pat. No. 3,454,347, a special dye is prepared by dissolving a dielectic and a coloring agent in a liquid, vacuum drying the liquid and grinding the resulting solid. This dye is then applied to a dry textile which is subsequently sprayed with water.
This type of process suffers from the disadvantage of necessitating the use of a special dye. Additionally, preparation of an acceptable dye for use with such a system involves a number of problems including the selection of a dielectric having quite a few special properties, such as a high electrical resistance and the property of not interfering with the penetration of the dye into the textile fibers. Another problem with such a process is the great quantity of pollutants expelled during the washing operation. The effluent of such a process necessarily contains the dielectric chemical.
In accordance with the present invention, a process far superior to conventional dyeing processes is provided. The above-mentioned inadequacies of prior art dyeing processes are greatly alleviated, resulting in substantial savings. Power requirements, necessary to maintain the dyebath at or near the boil are reduced considerably. Chemicals used to dye the cloth electrostatically are used more efficiently. This results in an effluent containing fewer waste products which must be paid for as well as treated.
Conventional textile dyes are used, and the absence of dielectric from the process results in an effluent free of dielectric pollutants. Use of a conventional dye is thus more economical from the standpoint of dyestuff cost and effluent treatment. Furthermore, there is no dielectric to interfere with the dyeing of the cloth.